The present invention pertains to a process for manufacturing a ball-and-socket joint housing by cold forming.
Ball-and-socket joints are used in the automobile industry especially for steering tie rods or in wheel suspensions, where they must withstand sometimes extreme weather effects as well as mechanical or chemical stresses over a very long life cycle.
The increasing need to design ball-and-socket joints as low-weight ball-and-socket joints conflicts with these requirements. It is known in practice that ball-and-socket joint housings can be manufactured from a blank consisting of wire material, which is forged into a joint housing after being heated in a plurality of consecutive steps. Even though this energy- and labor-intensive process makes it possible to manufacture high-strength ball-and-socket joint housings, forged components also always have the drawback of having a very high own weight.
A process for manufacturing a joint housing for ball-and-socket joints has become known from DE 195 36 035 A1, which can be manufactured as a whole by cold forming. An axial depression with the diameter exceeding the diameter of the internal thread to be prepared later is prepared in the blank by reverse cup extrusion in order to subsequently reduce only the threaded area to the thread root core diameter with simultaneous deformation of the jacket surface into a wrench contact surface. Additional methods, such as upsetting, cupping, punching, calibration of both the outer contour and the inner contour of the joint housing, are subsequently necessary to finish the joint housing described in the said document. Moreover, it is necessary to tap an internal thread after the forming operation and, on the other hand, an annular groove is to be turned in for fastening a sealing bellows. In addition, no real weight reduction can be expected with such a design.
The basic technical problem of the present invention is to provide a process for manufacturing a ball-and-socket joint housing, which makes it possible to produce a ball-and-socket joint housing manufactured as a whole by cold forming in a light-weight design by forming operations.
This technical object is accomplished by the features of patent claim 1. For preparation for the forming of the blank cut off, which consists of a bar or wire material, it is helpful in the sense of the present invention to first press a trough-shaped depression into same or to pretreat the surface of the blank in order to be able to subsequently perform the forming processes with the highest accuracy and quality. For example, the centering of the blank in the forming die can be facilitated by the aforementioned preparatory actions. The prepared blank, which is usually called a plate bar, is first provided with an axial depression in a first operation by means of reverse cup extrusion, the axial direction being defined by a longitudinal axis of the blank. After the preparation of the first axial depression with a first diameter in the blank, a second axial depression is likewise prepared by reverse cup extrusion in the first axial depression prepared before in another operation. The second axial depression has a larger diameter compared with the diameter of the first axial depression. The first axial depression is thus widened. Deformation of the material, which also leads to a reduction in the diameter of the first axial depression in at least some sections, takes place within the ball-and-socket joint housing being formed during the second reverse cup extrusion.
The reverse cup extrusion makes it possible to manufacture very thin-walled metallic hollow bodies. This method is utilized in the case according to the present invention in two consecutive steps in order to manufacture a ball-and-socket joint housing produced as a whole by cold forming, which is designed as a hollow body in a light-weight design. This light-weight design makes it possible to reduce the weight to a hitherto unknown extent. Moreover, compacting of the material is achieved during the reverse cup extrusion as a consequence of the flow processes taking place in the material, so that the necessary strength requirements are met as well.
The first axial depression thus forms a cavity in the ball-and-socket joint housing finished later, while the second depression prepared later forms the bearing pot of the housing, which is provided to receive the ball-and-socket joint components such as the bearing shell and the ball pivot mounted therein.
Further embodiments of the process according to the present invention are described in the subclaims.
For example, the axial length of the second depression may be made shorter than the length of the first axial depression corresponding to an embodiment of the process according to the present invention. This case will occur mainly in the case of very long ball-and-socket joint housings which are used, e.g., in axial joints on steering tie rods.
Moreover, it is possible in a simple and advantageous manner during the performance of the reverse cup extrusion operation to make an axial pin integrally on the ball-and-socket joint housing at the same time. Furthermore, the ball-and-socket joint housing may be provided at the same time with an outer wrench contact surface during this first reverse cup extrusion operation, so that need for additional operations can be eliminated and the ball-and-socket joint housing can be manufactured at a very low cost. The wrench contact surface will be used later, during the installation of the ball-and-socket joint housing in the motor vehicle, e.g., to attach a tool. However, it is, of course, also conceivable to form the wrench contact surface integrally only during the second reverse cup extrusion operation.
According to one embodiment of the process according to the present invention, the axial pin has a thread, which is can be made integrally on the axial pin, e.g., i.e., rolled or tapped into the axial pin.